Currently, many technologies in everyday use utilize radio frequencies to emit and receive information. These technologies then generate an electromagnetic field which, in proximity to a living being, is likely to interfere with the biological operations, in particular of the nervous system.
Several symptoms have been frequently observed in people exposed repeatedly to an electromagnetic field, namely headaches, increased stress, nervousness and irritability, sleep problems, increased tiredness, as well as weakened immune defenses, problems with concentration and memory, problems with the neuroendocrine-immune system and some fields could be the source of increased risks of cancer and miscarriage.
In this context, cellular telephones called “mobile” or “portable” are radiofrequency transmitters operating at frequencies of between 450 and 2700 MHz with a maximum power emission of between 0.1 and 2 Watts. Even though such transmitters are low-power types, the duration of their users' exposure exceeds several hours per day, but the influence may be increased because of their close proximity in use, in contact with the ear during telephone conversations or carried on the person, in a pocket, for the remainder of the time.
Given this, it is necessary to limit a user's exposure to the electromagnetic fields generated by a terminal, without this degrading the latter's operating conditions.
One solution is envisaged in document EP 1 981 324, describing a cellular telephone pouch made of a material that creates a barrier to protect the telephone from any radiation or emission. Said material is made of several layers formed from a weave of warp and weft threads, where one or the other is made of an electrically conductive compound, in particular metal in ribbon form such as brass, nickel or copper. However, such a shell blocks the electromagnetic radiation completely, both from and towards the telephone, which can then remain switched on but will be disconnected from the network's electromagnetic field and the other electromagnetic fields.
Another solution consists of a semi-rigid protective shell that limits the radiation of the electromagnetic fields coming from a cellular telephone. As described in document EP 0 915 572, said shell is made of elastomeric material, covered in or including a metal lattice or mesh, such as polyester covered in copper and nickel. Such a shell is not entirely satisfactory, however, as it only covers part of the telephone, limiting the electromagnetic radiation only at the location of the radio frequency emission and reception antenna.
An alternative solution consists of a textile for attenuating the electromagnetic radiation. As described in document WO 2002/05892, such a textile is made from textile fibers and at least one electromagnetic field attenuation compound, contained in the textile in a 5 to 15% proportion within said textile. In particular, the latter is made of woven fibers with which said attenuation compound is woven or incorporated, which may be firstly metallic, such as silver, gold, platinum or copper, or secondly a crystalline structure type of semiconductor containing in particular silicone, selenium, germanium or boron. In this way, by weaving it with a natural fiber such as wool or cotton or with a synthetic fiber such as polyester or acrylic, it is possible to manufacture a textile with a view to producing an item of clothing or a portion of an item of clothing, such as a pocket, through which electromagnetic radiation is limited.
However, a disadvantage of such a textile lies in the fact that it is complicated and costly to manufacture, utilizing costly materials. Moreover, the item of clothing blocks the radiation, disconnecting the telephone from the network.
Another solution from a related field is described in document WO 2008/044414 and concerns an apron for protecting from electromagnetic fields. In particular, such an apron is made of a multilayer structure, which gives it its ability to completely block the electromagnetic waves. In effect, the structure of such an apron constitutes a shield that the waves of an electromagnetic field cannot penetrate.
Such a shield is preferably designed to be used as protective clothing, in particular for persons who have a pacemaker, the operation of which is likely to be disrupted by an electromagnetic field. In this way, this apron makes it possible to block the radio waves and the electromagnetic fields, in particular coming from induction cooktops.
More specifically, the front and rear faces of its structure are covered in layers made of a woven synthetic or natural fiber material, notably, as an example, wool or cotton. It can be seen that the only purpose of these textile layers is to provide cover layers in front of and behind the apron, improving the finish so that the apron looks like an item of clothing. They are not arranged so as to play a part between the other layers.
Moreover, said structure is made of a copper absorption layer and of an aluminum blocking layer or “shielding sheet”. In addition, the copper layer may be in the form of a sheet, lined with iron or nickel, between 10 and 35 microns thick. Preferably, the 35-micron thickness provides sufficient shielding to absorb the magnetic field, while retaining a flexible characteristic of the garment. The role of this copper layer is therefore to absorb the magnetism from the electromagnetic field.
In addition, the aluminum layer acts as a reflector, using this material's characteristic of impermeability to electromagnetic radiation. It cuts the electromagnetic field that has not been absorbed by the copper layer.
Generally, the copper layer attenuates the electromagnetic field and the aluminum layer blocks the field thus attenuated. It should be noted that the copper and aluminum layers are separated by carbon sheets. These carbon sheets are obtained by polymerization so as to constitute a flexible and uniformly compact multilayer structure with the copper and aluminum layers; the cloth layers are in no way involved.
Thus, the structure of this device makes it possible to block electromagnetic fields with frequencies between 20 kHz and 2 Gigahertz (GHz), thanks to an aluminum layer for completely blocking the electromagnetic field. However, this device does not make it possible to simply reduce the electromagnetic field so as to provide for the operation of an electronic device, in particular a cellular telephone.